This section provides general background information related to the present disclosure and the background information is not necessarily prior art.
Automated process control systems are conventionally used in various industries, such as biotechnology, beverage, dairy, food, and pharmaceutical manufacturing. These systems rely upon the measurement of process parameters (pressure, temperature, flow rate, fluid level, etc.) which are sensed by sensor assemblies. These sensor assemblies not only sense the particular process parameter desired at that particular point in the process, but also transmit the sensed values of the parameter to the automated process control system for appropriate action by the control system. That is, the sensor assemblies typically have both a sensing function and a communications function. Prior art sensor assemblies are conventionally single integrated units (i.e., includes the sensor function and the communications/signal processing in a single physical housing). With conventional prior art sensor assemblies, the entire assembly must be replaced when the sensing portion fails.
The housing for conventional sensor assemblies vary widely depending upon various factors, including (1) type of process connection, (2) parameter range for operation, (3) signal output (e.g., 4-20 ma, digital or field bus), and (4) orientation of installation. Although it is possible to keep a complete inventory of the sensor assemblies needed to keep the process line functioning, that can be an expensive proposition which some industries typically forgo. For example, the dairy facilities frequently do not stock a complete inventory of sensor assemblies. If the proper sensor assembly is not available, for whatever reason, when an installed assembly fails, production must be shut down until the proper sensor assembly is obtained and installed. This can be an expensive inconvenience for companies located near sources of replacement sensor assemblies. It can become an even more serious inconvenience when the plant is located in remote areas or in emerging countries with limited infrastructure.
One possible solution is to replace only the sensing portion of the assembly, since that is the portion that typically fails. That would drastically reduce the inventory that would be required to maintain full production. But this presents a problem: how to calibrate the sensor assembly in the field. As noted above, the sensor assembly includes both a sensing function and a communication function. Calibration of the sensor assembly involves ensuring not only that the sensing portion is supplying signals at the desired levels for the particular process parameter value being measured, but also that the communication part of the sensor assembly properly recognizes the output of the sensing portion and accurately communications the proper value of the proper parameter to the automated process control system. Such calibration in the field can be difficult. Since field calibration is not a common occurrence, it is prone to error if attempted by a local technician who typically lacks the needed expertise and can be a cause of further delay and expense if done by a specialist, who typically must travel to the processing facility to effect the replacement.
In many industries, e.g., dairy or brewing, sensor assemblies are subjected to high levels of humidity and moisture in general. This operating environment can also be true for tropical locales, even for typically “dry” material processing systems. The electronics in sensor assemblies can be extremely sensitive to unwanted moisture. Unwanted moisture can enter existing sensor assemblies (and potentially damage the electronics) not only in high humidity conditions, but also when the housing for the assembly is dented or otherwise damaged in such a way as to interfere with any moisture seals which are built into the sensor assembly. Existing sensor assemblies typically have visual displays incorporated into the assembly for displaying to a user the value of the particular parameter being measured. These displays are typically seen through a transparent cover. In high humidity conditions, this cover can accumulate moisture, thereby obscuring the view of the visual display in conventional sensor assemblies. The transparent enclosure, of course, must also be attached to the sensor assembly housing in such a way as to prevent the passage of moisture to the interior of the housing, but this goal is not always satisfactorily achieved with existing sensor assemblies. Frequently it is not possible for the person installing the transparent cover to determine whether the cover has been properly installed on the sensor assembly housing or to determine whether a moisture-tight seal has been achieved.